Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

1. Rating of a domestic refrigerator is of the order of

10 tons

40 tons

5 tons

0.1 ton

2. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Brine

Ammonia

Carbon dioxide

3. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.67

0.6

0.376

4. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Above critical temperature

At critical Temperature

Much below critical temperature

5. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

6. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

7. The boiling point of ammonia is

-30°C

-77.7°C

-33.3°C

-10.5°C

8. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

9. A bootstrap air cooling system has

Three heat exchangers

Four heat exchangers

Two heat exchangers

One heat exchanger

10. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

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11. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Carnot

Reversed Rankine

Carnot

12. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

13. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Saturated liquid

Superheated vapour

Wet vapour

14. Which of the following cycles uses air as the refrigerant?

Carnot

Bell Coleman

Stirling

Ericson

15. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

5.12

1.25

16. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Zero

None of these

Negative

17. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

15 bar

30 bar

8 bar

18. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dew point temperature of air

Dry bulb temperature of air

Wet bulb temperature of air

19. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Miniature sealed unit

Centrifugal

20. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

A gas will never liquefy

Page 3 of 4

21. The capillary tube, as an expansion device, is used in

Water coolers

Room air conditioners

Domestic refrigerators

All of these

22. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Refrigerant cooling tubes

Evaporator tubes

Capillary tubes

23. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 9

1: 3

9: 1

24. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Receiver and evaporator

Evaporator and compressor

Condenser and receiver

25. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

26. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Less

Equally

Unpredictable

27. Freon group of refrigerants are

Non-inflammable and toxic

Inflammable

Toxic

Nontoxic and non-inflammable

28. The freezing point of sulphur dioxide is

-135.8°C

-75.2°C

-56.6°C

-77.7°C

29. For obtaining high COP, the pressure range of compressor should be

Any value

Optimum

Low

High

30. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Page 4 of 4

31. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always more than unity

Any one of the above

Always less than unity

32. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

33. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

Takes place at constant entropy

34. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Large latent heat

High risibility with oil

Low boiling point

35. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

Same

More for small capacity and less for high capacity

36. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Condenser, absorber and separator (rectifier)

Evaporator

Condenser

37. The curved lines on a psychrometric chart indicates

Relative humidity

Wet bulb temperature

Dry bulb temperature

Dew point temperature

38. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Sub-cooling or under-cooling

Super-cooling

Normal cooling

39. Most thermostatic expansion valves are set for a superheat of

5°C

15°C

10°C

20°C

40. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

4.33

2.33

3.33

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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